The invention relates to a device for dispensing of a powdered drug preparation by inhalation. The device is in particular a multiple-dose device without propellant gas, equipped with a metering means which dispenses doses from a powder container. A device such as this is usable, for example, in the treatment of asthma.
The administering of powdered drug preparation by inhalation from an inhaler is commonly known. Multiple-dose type power inhalers comprising a powder container and a metering member which measures and dispenses a unit dose are also known, for example from patent publications GB 2165159, EP 79478, and EP 166294. In these devices, a series of dosing recesses are notched into the surface of a cylindrical metering member, and the said member is disposed in a chamber of precisely the same shape. When the metering member is rotated, the dosing recesses in turn will move first to a position in alignment with the powder container for being filled and thereafter to a position in alignment with the inhalation channel, whereupon a unit dose will fall by gravity from the dosing recess into the inhalation channel. Thereafter the dose of medication is inhaled from the inhalation channel. These devices have the drawback that they make overdosing of the medication possible by allowing the dispensing of a plurality of doses in succession into the inhalation channel, whereby a multiple dose may be drawn by one inhalation. Inhalation devices having a metering plate movable between filling and dispensing position are described e.g. in patent publications WO 92/10229, U.S. Pat. Nos. 5,113,855, 2,587,215, EP 546996, WO 94/04210 and U.S. Pat. No. 5,161,524. However, also these devices suffers from a drawback that they make overdosing possible by allowing the dispensing of a plurality of doses into the inhalation channel.
Attempts have been made to solve this problem by using dispensing systems in which the dosing recess will not be emptied into the inhalation channel by gravity but, instead, the dose of medication is inhaled directly from the dosing recess, such recesses having been notched into the surface of a metering member having the shape of a cylinder, a cone or a truncated cone, as disclosed in patent publications WO 92/00771 and WO 92/09322. Also in these devices, a metering member having the shape of a cylinder, a cone or a truncated cone is disposed in a chamber having precisely the same shape. When the metering member is rotated, the dosing recesses will move first to a position in alignment with the flow container for filling, and then to the inhalation channel, which is shaped so that the dosing recess will be emptied under the effect of the air flow being inhaled, and thereafter, having rotated through a full 360.degree., back to a position in alignment with the flow container. The lower surface of the chamber wall may also have an emptying aperture from which any powdered medication possibly left in the dosing recess will fall out during the said rotation.
In the rotating dispensing devices described above, the distance from the filling position to the inhalation position is less than 90.degree. of a circle arc. Since the metering member is, for purposes of metering precision, disposed within a chamber of the same shape, and since it has to be rotated through 360.degree., of which at least 270.degree. are useless for the actual function of the inhaler, in these devises particles will inevitably fall onto the slide surface between the metering member and the chamber. Thereby the rotation of the highly sensitive metering member will be disturbed and may even be completely obstructed. The metering member jamming in the chamber will hinder the functioning of the whole device. Vigorous shaking or tapping will only increase the jamming, as more powder flows into the gap between the chamber and the metering member.